The present invention relates to a solid-state image pickup device which can increase light-gathering efficiency to a light receiving sensor unit to enhance the sensitivity characteristic thereof.
Recently, solid-state, image pickup devices have made further progress in a compact design and a high-density design of pixels, and this progress in the microstructure design has caused reduction in the light receiving area in which light is received, thereby inducing degradation of characteristics such as reduction in sensitivity, etc. As a countermeasure to the reduction in sensitivity, it has been proposed and practically used to provide an on-chip lens or an in-layer lens to enhance the light gathering efficiency at the light receiving sensor unit.
However, a solid-state image pickup device in which an in-layer lens is formed of material having high refractive index has the following problem.
In the case where the in-layer lens is formed of P—SiN having a refractive index of about 2.0 (silicon nitride based on the plasma CVD method), since a color filter layer formed on the in-layer lens usually has a refractive index of about 1.6, there is large difference in refractive index between the in-layer lens and the color filter layer, and thus reflection occurs at the interface between the in-layer lens and the color filter layer, so that the sensitivity characteristic is reduced. The reflection due to the difference in refractive index is inherently introduced from the wave equation.
An interlayer film which is subjected to a reflow treatment, etc. is formed under the in-layer lens, and BPSG (boron phosphorus silicate glass) having a refractive index of 1.45 or the like is normally used as the interlayer film because it is subjected to the reflow treatment, etc. Accordingly, as in the case of the refractive index difference between the in-layer lens and the color filter layer, the large difference in refractive index occurs between the in-layer lens and the interlay film and reflection also occurs at the interface therebetween, so that the sensitivity characteristic is reduced.